The present invention relates generally to separable electrical connectors for electrical power distribution systems. More specifically, the invention relates to separable electrical connectors adapted to be threadedly engaged, including transformer bushing well inserts and bushing well receptacles. Still more specifically, the invention relates to an electrically conductive connector having self-contained means for limiting the amount of rotational torque which is applied to the threaded stud of a second electrically conductive connector during the threaded engagement of the two connectors. The present invention also relates to a threadedly engageable electrical connector which is used in circumstances where the relative orientation of the electrical connector when it is securely engaged is important for its intended purposes.
In electrical power distribution systems, and particularly in systems using pad mounted type distribution transformers and switchgear to provide electrical power to commercial sites and residential dwellings, it is often desirable to provide an electrically conductive but separable connection between a high voltage power source feeder cable and an input bushing well of a transformer. For example in such a situation where a pad mounted transformer is used, a high voltage power source feeder cable typically emerges from beneath its buried position in the ground and passes up through a portion of the base of the pad mounted distribution transformer and into an open but enclosable space within the transformer. Once above the ground, the end of the power feeder cable is electrically and mechanically secured to an elbow connector. Bushing well inserts, such as load break inserts and feedthru inserts, are mounted in the walls of the transformer enclosure and are designed to matingly receive elbow connectors and complete the electrical and mechanical connection between the elbow connector and the internals of the distribution transformer. An electrical path connection is provided by means of a threaded stud which is part of the bushing well receptacle and which acts as a male connector. To make a connection with the elbow connector which also is a male type connector, an insert is first threadedly secured to, that is screwed onto, the threaded stud of the bushing well receptacle. Then the elbow connector is slidably engaged into a corresponding female connector in the insert.
By virtue of historical development, the vast majority of bushing well receptacles have studs which are 3/8" in diameter. One problem which may occur in the threading of the insert onto the threaded stud of the bushing well receptacle is that if torque continues to be applied after the insert has been completely threaded onto the bushing well stud, the threaded stud will yield and possibly break. This over-torquing of the threaded stud of the bushing well receptacle may cause a loss in the integrity of the mechanical and electrical connection between the insert and the transformer bushing well. If the bushing well stud is sufficiently over-torqued, the threaded stud may shear off completely, thereby requiring a replacement of the bushing well receptacle. This often requires removal of the entire transformer unit to another location for repair.
An additional problem may arise when a feedthru insert is used. A feedthru (or double bushing) insert has a pair of legs projecting away from the transformer when the feedthru insert's third leg has been threadedly connected to the stud of a transformer bushing well receptacle. Each of the projecting twin legs contains a female connector which is electrically connected internally within the feedthru housing to the female connector in the other twin leg as well as to the female connector which is threadedly engaged to the stud of the bushing well receptacle. When the feedthru insert has been torqued into fixed operative threaded engagement with the stud of the bushing well receptacle, that is, when the feedthru insert has been screwed completely onto the bushing well stud, the twin legs often are not suitably oriented or aligned so as to facilitate, or perhaps even permit, connection to the elbow connectors attached to the power system cables. This is because the power cables rising up through the base of the transformer are relatively stiff and may be of such length that the regions of movement for each of the elbow connectors may not include the twin legs of the feedthru insert so that connections between the twin legs and the elbow connectors can not be made. Or, the outwardly projecting twin legs may be oriented with respect to each other such that one of the legs upon connection to a first elbow connector may interfere with the connection of another elbow connector to the remaining second leg. In the past these situations often have necessitated adjusting the position of the outwardly projecting twin legs by unscrewing or loosening the third leg of the insert at the threaded stud of the transformer bushing well receptacle until the twin legs were rotated into proper alignment for connection with their elbow connectors.
A feedthru insert which allows adjustment of the orientation of the twin legs without unscrewing or loosening the insert on the threaded stud is shown in U.S. Pat. No. 4,203,641. The double bushing insert shown in that patent incorporates an annular shaped, resilient, "louvered" contact element 122 which enables the twin legged portion of the insert, after threaded engagement of the third leg with the bushing well stud is completed, to be partially rotated circumferentially with respect to the bushing without unscrewing the third leg from the bushing well stud (columns 7, lines 22-41); however, the insert has no means for limiting the amount of torque applied to the bushing well stud after completing the threading engagement of the insert onto the stud and further the rotational movement of the twin legs circumferentially around the bushing well receptacle is limited to approximately an arc of 180 degrees.